1. Field of The Invention
This invention relates to a room temperature vulcanizable organopolysiloxane composition which is useful as a sealant for buildings.
2. Description of the Prior Art
One pack-type room temperature vulcanizable (hereinafter sometimes referred to simply as RTV) organopolysiloxane compositions are in general-purpose use in the electric and electronic fields and also in building fields. This is because they have advantages in that the compositions are vulcanized, by the action of moisture in air, by merely pushing out from tubes or cartridge-type containers and are thus easy in use and that the compositions are unlikely to corrode electric and electronic parts therewith.
Since silicone-based sealants and adhesives exhibit good weatherability, adhesiveness, durability and the like properties, the RTV organopolysiloxane composition has wide utility in the field of buildings for waterproofing of metal curtain walls, concrete curtain walls, aluminum sashes, ALC (autoclaved lightweight concrete) panels, glass window frames and the like which are ordinarily used as outer walls of buildings and also as airtight sealants and adhesives for various types of building materials. Especially, when the composition is applied as a waterproof sealant, there is a demand for the composition which is able to follow up a stress which would be imposed thereon owing to the difference in temperature, wind or earthquake.
For instance, usual practice is to use a low modulus sealant as a joint sealing material for buildings having great movements. Known low modulus sealants include, for example, those which make use of bifunctional organosilanes or organosiloxanes having two hydrolyzable groups and trifunctional or higher functionality-bearing organosilanes or organosiloxanes having three or more hydrolyzable groups, with which diorganopolysiloxanes having a silanol group at both ends of the molecular chain are cured. However, such a low modulus sealant as set out above has a difficulty in stabilizing the physical properties after curing. Especially, it is difficult to stably keep the low modulus over a long time. Further, the reactivity of the hydrolyzable groups of the trifunctional or higher functionality-bearing organosilane or organosiloxane is greater than that of the hydrolyzable groups of the bifunctional organosilane or organosiloxane. Eventually, the curing reaction of the trifunctional or higher functionality-bearing organosilanes or organosiloxanes proceeds more rapidly. This involves a great difficulty in properly controlling the working life of two-component sealants, thus requiring to overcome this difficulty in use.